The Applicant has previously described a number of different maintenance and ink delivery systems for maintaining healthy inkjet nozzles in pagewide printheads. In order to print optimally from an inkjet printhead, at least two requirements must be met: (1) the printhead face should be free of any flooded ink; and (2) the inkjet nozzles should be free of any viscous plugs of ink, particles/fibers and air bubbles.
In order to meet the first requirement, printheads typically require wiping to remove flooded ink. Wiping may be either along a longitudinal extent of the printhead (see, for example, WO2013/059853) or transversely across the printhead (see, for example, WO2011/143699). The wiper may be wet or dry, depending to some extent on the characteristics of the ink (e.g. dye-based or pigment-based ink).
In order to meet the second requirement, printers are typically equipped with an ink delivery system, which can force ink from nozzles so as to remove air bubbles and viscous ink plugs. For example, WO2011/143698 describes an ink delivery system having a pump, which in combination with a pinch valve, is used to force ink through inkjet nozzles in a pressure-priming operation. Subsequent spitting of ink into a spittoon may be used to maintain healthy nozzles until the printhead is ready to print.
Pigment-based inks generally present greater challenges for maintenance systems than dye-based inks. Since pigments are prone to precipitate from inks and clog wet wipers, dry wiping is usually the only option for wiping pigment-based inks. Dry wiping requires wiping a relatively clean, dry portion of wiping material over the printhead. Therefore, dry wiping usually requires a long length of available wiping material to provide a predetermined number of wipes, which is sufficient for the lifetime of the printhead. Accommodating a long length of wiping material is problematic for the overall design of inkjet printers. Moreover, in printers have relatively closely-spaced printheads (e.g. the digital inkjet press described in U.S. Pat. No. 8,529,014 or the wideformat printer described in U.S. Pat. No. 8,567,899, the contents of which are incorporated herein by reference), accommodating a length of wiping material for each printhead is particularly problematic in the relatively small volume of space available for maintaining each printhead.
A further problem with wiping printheads is the potential for damage to sensitive inkjet nozzles due to shear forces from the wiper or loose fibers becoming lodged in nozzles.
It would be desirable to provide a maintenance system for a printhead, which is suitable for wiping pigment-based inks and which can be accommodated in a relatively small volume of space.
It would be further desirable to provide a maintenance system, which minimizes an amount of wiping material employed over the lifetime of a printer.
It would be further desirable to provide a maintenance system, which minimizes the risk of damage to the printhead.
It would be further desirable to provide a means for priming inkjet nozzles, which places fewer design constraints on ink delivery systems.